The interactions between cardiac microsomes enriched in fragmented sarcoplasmic reticulum (SR) and Ca2 ion will be examined in an attempt to clarify the mechanisms that control myocardial contractility. The actions of Ca2 ion-ionophores will be characterized to define the reaction mechanisms by which Ca ion is transported into the SR. The possibility that the ionophore-treated SR, which exhibits a Ca2 ion- triggered Ca-release, may serve as a model for the SR at the onset of cardiac systole will be explored and the role of prostaglandins in these systems will be examined. The oxalate-dependence of oxalate- facillitated Ca-uptake will be characterized kinetically in an effort to quantify the rate constants of this process. Studies of the actions of cardiac cyclic AMP-dependent protein kinase (PK) will continue with attempts to isolate and purify phospholamban, the phosphorylation of which accompanies increased Ca- transport rate. The localization of this phosphoprotein in the SR will be examined and its functional role will be characterized in native, partially dissociated and reconstituted SR. The acyl-phosphate ATPase intermediate of the SR will be quantified in PK-stimulated cardiac microsomes and the effects of PK-stimulation on its formation will be examined. The role of phosphatases in controlling the dephosphorylation of phospholamban will be characterized, a correlation will be sought between dephosphorylation of phospholamban and loss of Ca-transport stimulation, and the system controlling this phosphatase will be studied. The mechanism of PK-induced Ca-transport stimulation will be characterized in terms of the kinetic model described above. Studies of the cardiac sarcolamma will be carried out in an attempt to identify and characterize a PK-mediated control system that regulates Ca-entry during systole.